Git's Staging Area — What Actually Happens Between `git add` and `git commit`

Git utilizes a three-layer model consisting of the working directory, the staging area, and the repository. Changes must progress through these stages before becoming part of a commit. Meanwhile, deploying AI coding agents across isolated Git worktrees reveals that while filesystems are separate, they share a single object database and branch namespace. This shared architecture can cause ref corruption and silent failures when multiple agents execute Git commands concurrently, necessitating a deep understanding of shared state hazards.